after installing civicrm 5.49.3 via composer on drupal 9.3.14, I have a problem with GuzzleHTTP. Can you advise me on how to fix this problem.

The website encountered an unexpected error. Please try again later. Error: Undefined class constant 'VERSION' in GuzzleHttp\default_user_agent() (line 136 of vendor/guzzlehttp/guzzle/src/functions.php). GuzzleHttp\default_user_agent() (Line: 52) Drupal\Core\Http\ClientFactory->fromOptions() call_user_func_array(Array, Array) (Line: 258)

1 Answer 1


What it sounds like is your site has a module or something that includes guzzle v7 somewhere, and the one in vendor is v6. So what's happening is that it loads src/functions.php from the v6 one, but loads ClientInterface from the v7 one, and so there is no VERSION property.

So you need to find where guzzle 7 is and decide what to do from there. You can try find . -name BodySummarizer.php which is a file in v7 that isn't in v6.

  • Drupal 9 allows for guzzle 6 or 7. CiviCRM asks for ^6.3, so that's presumably the one in vendor. Seems most likely that you've got a CiviCRM extension that packaged guzzle (7), but you might also have a badly packaged Drupal module. As a quick fix, you could try installing guzzle 7 as 6 (i.e. that composer trick), it's possible that civicrm will work okay with 7.
    – Alan Dixon
    Jun 7, 2022 at 20:26

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